Fluid pressure device



March 20, 1945. E. n. FITCH FLUID PRESSURE DEVICE Filed April 30, .1943

Ellery Ridch.

Patented Mar. 20, 1945 Ellery 1t. Fitch, Elyria, Ohio, ascignor to Bendix- Westinghouse Automotive Air Brake Company, Elyria, Ohio, a' corporation of Delaware Application April 30, 1943, Serial No. 485,225

16 Claims. (01. 121-38) This invention relates to control mechanisms and more particularly to remotely controlled fluid pressure operated mechanisms especially adaptable for use in connection with the control of 1 throttle valves on motor vehicle engines.

It has heretofore been proposed to employ fluid motors of the type having cylinders and pistons for actuating such throttle valves by fluid pressure, but due to the inherent friction between the piston and the cylinder walls, considerable difllculty has been experienced in obtaining smooth and satisfactory control.

It is accordingly an object of the present invention to provide a fluid motor for actuating such mechanisms so constituted as to avoid the above disadvantages.

Another object of the invention is to provide, in a fluid motor of the above type, an arrangement. for providing smooth and efficient action throughout the entire range of operation.

Yet another object of the invention is to provide, in a fluid motor of the above type, resilient means for opposing movement of the piston so constituted as to permit the rate of pickup of the resilient means to be increased and decreased as desired during diiferent portions of the piston stroke.

tion of the limits of the invention, reference for this purpose'beinghad to the appended claims.

In the drawing wherein similar reference characters refer to similar parts throughout the several views;

Fig. 1 is a diagrammatic view, partially in section, of a control mechanism constructed in accordance with the principles of the present invention, and

Fig. 2 isan axial sectional view of a modified form of a fluid motor adapted tobe employed A further object of this invention is to provide, in a fluidmotor of the above type, means for insuring a greater travel during theIatter portion of the piston stroke during a given pressure increase than occurs during a like pressure increase on the piston during the first part of the stroke.

Still another object of the invention is to provide, in a fluid motor of the above type, resilient means for opposing movement of the piston, so constituted as to provide a high rate of pickup of the resilient means during the initial portion of been set forth hereinafter by way of description and exempliiic'ation in the accompanying drawing. It is to be expressly understood, however, that the drawing is employed for purposes of illustration only, and is not designed as a definiin the systemillustrated in Fig. 1.

Referring more particularly to Fig. 1, the system illustratedincludes a source of fluid pressure or-reservoir 5 adapted to be supplied with fluld'pressure from a suitably driven compressor 6, through the medium of a conduit 1, fluid pressure being-supplied from the reservoir 5 under the control of the operator to a fluid motor, generally designated as 8, through the medium of a conduct 9, a control valve [0, and a conduit ll leading therefrom to the fluid motor.

The control valve I0 is provided with an opdegree of movement of the control pedal. It will be further understood that with the control pedal in the position shown, the valve mechanism serves to establish a connection between conduits I I and I! to connect the fluid motor with atmosphere and to prevent communication between the conduits 9 and II, while on downward movement of the control pedal, the valve prevents communication between the conduit ii and the exhaust port l3 and establishes a connection between conduits 9 and H in order to supply fluid pressure to the motor 8 from the reservoir 5.

In the drawing, the fluid motor 8 is adapted to control the operation of an engine' l4 provided with, an inlet manifold 15 and a throttle valve i6 pivotally mounted therein by means of a shaft H, the shaft being provided with a throttle operating lever II as shown. This lever is actuated by means of the fluid motor 8 as will be described hereinafter, the motor 8 being provided with a cylindrical casing l3, the right end of the casa connecting member or rod 23 slidably mounted therein and connected at its left end to the lever It by means of a pivot pin 24 engaging a. slot 26 in the lower end of the lever. In order that the throttle may be normally maintained in closed position, a retracting spring 26 is interposed between the right face of the plate 2| and the left face of a shoulder 21 formed on the rod 23.

this arrangement servinmin' connection with a stop 28 formed on the connecting rod and abutting the left end of the plate 2|, to preload the spring 26 in order to normally maintain the connecting rod in retracted position with a predetermined degree of force depending on the degree of compression of the spring;

A piston. 29 is slidablypmounted -in a bore 36 formed in the casing I9, and is adapted to impart motion to the connecting rod 23 through the medium of a spring 3| interposed between the right side of the shoulder 21 and the left face of plate 32 carried by an extension 33 formed on the piston. An extension 34 of reduced diameter is formed on the right end of the connecting rod 23 which is slidably mounted in a bore 35 formed in the extension 33, separation of the parts being prevented by means of a pin 36 mounted in the right end of the extension 34 and adapted to slide in slots 31 formed in the extension 33. The pin 36 is so located with reference to the parts as to initially precompress the spring 3| with a force which may be equal to, but preferably less than, the force exerted by the spring 26 due to the precompression of the latter, the tendency thus being, on application of fluid pressure to the right end of the piston, for the piston to move to the left and partially compress the spring 3| prior to movement of the connecting rod 23. The piston is provided with a sealing member orcnp 33, and it will be understood that movement of the piston is normally opposed by a force corresponding to the friction between the piston 23 and the wall of the cylinder as well as by a force due-to the friction of the sealing member 38 on the cylinder wall, and the degree of preloading or precompression of the spring 3| is preferably so chosen as to be less than the preloading of the spring 26 and slightly greater than the total frictional force opposing initial movement of the piston, the spring 26 thus acting to normally maintain the rod 23 in the retracted position shown, and the spring 3| serving to maintain the piston in the position shown with the pin 36 in the left end of the slots 31.

As heretofore stated, the control valve I is of the preloaded type, initial operation of the control pedal |2 serving to immediately supply a predetermined pressure to the casing |9, and the preloading of the valve I0 is preferably so arranged as to initially admit to the casing a pressure which, acting on the area of the piston 29, is just suificient to overcome the force exerted by the preloaded spring 26, initial operation of the pedal |2 thus tending to result in immediate slight movement of the connecting rod 23 to the left to initially operate the throttle valve, the application of pressure to the casing l3 thereafter directly being proportional to the degree of further movement of the pedal l2.

In view of the relationship of the force initially exerted by the springs 26 and 3| it will be understood that on application of pressure to the easing sumcient to Just overcome the tension of the spring 26, this pressure will also be suflicient to overcome the frictionof the pistonand sealing cup as well as the tension of the spring 3|, in order to permit the piston to immediately move to the left with relation to the connecting member 23, and since the friction of motion of a piston or this type is normally less than the static friction, it will be apparent that after initial movement of the piston, this friction will decrease and the piston will respond with greater sensitivity to additional increments of pressure supplied to the casing. Thus the piston will be in motion before movement of the connecting rod 23 to the left occurs, and the initial Jerk which often occurs in mechanisms or this kind when the piston tends to stick in retracted position, will be substantially eliminated. Likewise, in the event the piston tends to move rapidly to the left as soon as the frictional force is overcome, the spring 3| will tend to absorb the shock which would otherwise be imparted to the rod 23 when this action occurs, thus preventing erratic operation of the throttle valve of the enginer It will also be understood that the dimensions of the spring 3| may be so chosen in relationship to the dimensions of spring 26 as to permit the spring 3| to be effective throughout the entire range of movement of the connecting rod 23 and the piston 29 in order to provide a resilient connection between the piston and rod at all times. In the event this action is not desired in a particular installation} the spring 3| may be so constructed as to permit the plate 32 to engage the shoulder 21 when the valve III is operated to initially supply fluid pressure to the casing |9, in order to provide a so-called hammer action on the connecting rod 23 in order to overcome any slight friction which may exist in the operation of the connecting rod or the throttle mechanismconnected thereto. With regard to the desirability of preloading the spring 3| suiiiciently to overcome the friction of the piston and sealing cup, it will be seen that this is necessary in order to insure that the piston will always return to the position shown in the drawing :an release of fluid pressure from the cas- In connection with the construction of a fluid motor such as shown in Fig. 1, it has been-found desirable in the past under certain conditions of operation, to provide means for increasing the rate at which the retracting spring force increases after the piston has travelled through a predetermined distance, and this has been accomplished by the use of additional springs so constituted as to be picked-up by the piston or connecting rod after the predetermined travel has occurred, the result being that during the initial portion of the stroke the rate of spring force increase is that of the first spring while the rate during the latter portion of the stroke is the combined rate of both .springs. It is pointed out, however, that a reverse action can be obtained wherein the rate of force increase of the retracting spring mechanism is greater during the initial portion of the stroke than during the latter portion of the stroke, and another embodiment of the invention is illustrated in Fig. 2, so constituted as to provide this desirable type ofoperation.

As shown in the drawing, this alternative form 2,s71,e1a Q 2 crease the rate of the spring system after the of fluid motor is provided with a casing is connected at its right end with conduit ll through the medium of ports and closed at the left end by means of a plate 2| having a connecting rod 28 slidably mounted in the bore 22, the left end of the rod being connected for actuation of the throttle valve 18 in the same manner as shown in Fig. 1. The motor is likewise provided with a piston 28 connected with the rod 23 through the medium of a lost motion mechanism identical with that shown in Fig. l, as well as through the medium of a spring 3i, likewise arranged in the same manner as in Fig. l.

In order that the connecting rod may be normally maintained in retracted position, a plate 21 is mounted on the connecting rod, and a second plate 39 is carried by the casing It, as shown, and provided with a centrally located bore 4lifor permitting unobstructed movement of the con- .necting rod, movementof the plate 38 to the right being prevented by means of a shoulder 4| formed in the casing. A spring 42" is interposed between the plate 2| and the plate 21 tending to force the rod 23 to the right, and a spring 43 is interposed between the plate 2'! and the plate 39 tending to move the rod 23 to the left, the relationship of these springs being such that the rod 23 is normally maintained in the position shrown with both of the springs partially compressed.

As has been heretofore stated, the rate of spring force increase during movement of the connecting rod 23 to the left in the event the spring 42 only were used to position the connecting rod, would be the rate of the spring 42, but it has been found that when this spring is opposed by the spring 48, with both of the springs in a-compressed state, the effective spring rate is the sum of the rates of change in force of the two springs. The spring 43 is so dimensioned, however, as to be fully extended when the connecting rod has moved to the left through a predetermined distance, the spring thus being ineffective to impart force to the connecting rod through plate 21 during further travel of the connecting rod; thus providing a construction wherein the rate of change of force exerted by the spring system is greater during the initial part of the stroke than it is during the balance of the stroke, since the force exerted by one spring is decreasing as the force exerted by the other increases, the result being that the degree of travel of the connecting rod in response to a predetermined pressure increase in the casing during the initial portion of the stroke is less than the travel of the connecting rod during the latter portion of the stroke in response to an equal increase in pressure in the latter range. It will be apparent that the spring 43 can be so designed as to become ineffective at any desired point in the stroke.

By combining a plurality of springs in the manner indicated in the drawing, the rate of force change of the spring system may be varied as desired during different portions of the stroke. By way of example, an additional spring 44 may be interposed between the plate 38 and the plate 21 and so dimensioned as to become ineffective before the spring 43 becomes inefiective, thus providing an additional step at which the rate of the spring system is different from that occurring either during the first or the last portion of the stroke. If desired, the action of the spring system may be varied by a further spring 45 which may have a different rate from any of the other springs, andif it is desired to subsequently inconnecting rod has moved through a predetermined distance. an additional spring 46 may be provided, so dimensioned as to be picked-up by the plate 21 after the piston has travelled through a predetermined distance in order to again increase the spring system rate. As indicated in the drawing, another spring 41 may be interposed between plates 21 and having still different characteristics from the springs 43 and 44, various combinations of the above springs arranged on either side of the plate 21 with varying degrees of compression, varying .lengths and varying rates providing any desired rate of force change in the spring system during any portion of the connecting rod stroke.

As heretofore stated, the connecting means between the piston 28 and the connecting rod 23 is arranged in the same manner as shown in Fig. 1, and for the same purpose, and in order to provide the same type of operation and to obtain the 'advantages inherent in this arrangement, the

springs 42, 43, 44, 45. 46 and 4] are so arranged as to resist initial movement ofthe connectin a rod to the left with a predetermined force, the

plication of fluid pressure thereto, for the same reasons stated in connection with Fig. 1.

It will be readily apparent from the foregoing description, that fluid pressure control mechanism of novel design has been provided, wherein the fluid motor is so constituted as to overcome 'or minimize the effects of piston friction, and further so constituted as to provide this desirable type of operation under all ordinary conditions of service. As more particularly illustrated in Fig. 2. novel means have also been provided retaining the advantages of the mechanism illustrated in Fig. 1, and at the same time providing a construction having resilient means for normally maintaining the actuating means in retracted position, so constituted as to permit the effective rate of the spring system to either increase or decrease at any desired point in the stroke. While the two described embodiments of the invention have been illustrated as applied to the control of the throttle mechanism of an engine, it will be readily understood that control systems of the type illustrated and described may be readily adapted to the control of other devices if so desired.

While two modifications of this invention have been described and illustrated, it is to be expressly understood that the invention is in no way limited thereby and thatvarious changes and modifications may be made therein without departing from the scope of the invention, for

the limits of which reference is had to the appended claims.

What is claimed is:

l. The combination with a source of fluid pressure and a device to be actuated, of a fluid motor member for exerting a predetermined force to normally maintain the latter in retracted position, resilient-means for connecting said element and member for permitting relative movement therebetween prior to movement of said member when fluid pressure is supplied to said casing, and means including a substantially frictionless lost motion connection between said member and element for precompressing said second resilient means, whereby the latter opposes relative movement of the member and element with a force less than said predetermined force and greater than the friction force between the element and casing. I

2. The combination with a source of fluid pressure and a device to be actuated, of a fluid motor having a casing adapted to receive fluid under pressure from said source, a piston slidably mounted in said casing and subjected to the pressure in said casing, an actuating member connected with said device, preloaded resilient means for normally maintaining said member in retracted position with a force greater than the friction force between the piston and easing, means including a resilient member and a substantially frictionless lost motion connection connecting said actuating member and piston for movement of the former when the pressure in means associated with said member and piston,

for insuring movement of the latter prior to saidcasing exceeds a predetermined value including a preloaded springinterposedbetween said casing and member 'fornormally maintaining the latterin retracted position with a predetermined force and a preloaded spring interposed between said member and piston for opopposing relative movement therebetween with a force greater than said friction force and less than said first named force.

3. The combination with a source of fluid pressure and a device to be actuated, of a fluid motor having a casing adapted to receive fluid under pressure from said ,source, a piston slidably mounted in said casing and subjected to the pressure in said casing,'an actuating member connected with said device, a preloaded spring interposed between said casing and member for normally' maintaining the latter in retracted position with a force greater than the friction force between the piston and easing, a substantially frictionless lost motion connection between said piston and member for freely permitting limited relative movement. therebetween, and resilient means interposed between said member and piston for opposing said relative movement with a force greater than said friction force and less than said first named force.

4.: The combination with a source of fluid pressure and a device to be actuated, of a fluid motor having a casing adapte to receive fluid under pressure from said source, a piston slidably mounted in said casing and subjected to the pressure therein, and means for connecting said piston and device including a connecting member and means associated with said memberand piston for insuring movement of the latter prior to movement of the former when the pressure in said casing exceeds a predetermined value including a preloaded spring interposed between said casing posing relative movement therebetween with a force less than said predetermined force and greater than the frictional force opposing movement of said piston in said casing, and a substantially frictionless lost motion connection between said member and piston for effecting the preloading of said second named spring.

'6. The combination with a source of fluid pressure and a device to be actuated, of a fluid motor having a casing adapted to receive fluid under pressure from said source, a piston slidably mounted in said casingv and subjected .to'the' pressure therein, means for connecting said piston and device including a connecting member, a

means associated with said member and'piston for insuring movement of the latter prior to.

movement of the former when the pressure in said casing exceeds a predetermined value including a preloaded spring interposed between said casing and member for normally maintaining the latter in retracted position with a preposing relative movement therebetween with a force less than said predetermined force, and valvular means for controlling the pressure supplied to said casing from said source having a controlling element operable on' initial movement to supply' a pressure to said casing suflicient to move said piston against said lesser force and operable on further, movement to. increase the pressure in said casing in direct proportion to the degree of said further movement.

7. The combination with a source of fluid pressurev and a device to be actuated, of a fluid motor having a casing, a piston slidably mounted in said casing and subjected to the pressure of fluid therein, means for connecting said piston and device, resilient means for maintaining said piston in retracted position with a predetermined force,-and resilient means effective through a means and ineflective during the balance of the and member for normally maintaining the latter in retracted position with a predetermined force, a preloaded springinterposed between said member and piston for opposing relative movement therebetween with a force less than said predetermined force and greater than the friction force between said piston and casing, and a substantially frictionless lost motion connection between said piston and member for insuring preloading of said second named spring to exert said second named force.

5. The combination with a source of fluid pressure and a device to be actuated, of a fluid motor having a casing adapted to receive fluid under pressure from said source, a. piston slidably stroke, whereby the fluid pressure necessary to move the piston during the first portion of the stroke is proportional ,to the combined pick-up of the two resilient means and is proportional to the pick-up of the first named resilient means during the latter portion of the stroke.

8. The combination with a source of fluid pressure and a device to be actuated, of a. fluid motor having a casing, a piston slidably mounted in said casing, and subjected to the pressure of fluid therein, means for connecting said piston and device, a spring for maintaining said piston in retracted position with a predetermined force and for opposing movement of the piston in one direction throughout the entire piston stroke, and a second spring tending to move the piston in the opposite direction during a portion of the stroke with a force initially equal to or less than said predetermined force, whereby the pressure increment in the casing necessary to move the piston a predetermined distance during said portion of the stroke is greater than that necessary to move the piston through the same distance during the balance of the stroke.

9. The combination with a source of fluid pressure and a device to be actuated, of a fluid motor having a casing, a piston slidably mounted in said casing and subjected to the pressure of fluid therein, means for connecting said piston and device, and a pair of opposed preloaded springs associated with said casing and piston for op-' posing movement of the latter in one direction by a force corresponding to the difierence in the forces exerted by the two springs, one of the springs being efiective throughout the entire pistonstroke and the other being effective during a portion of said stroke.

10. The combination with a source of fluid pressure and a deviceto be actuated, of a fluid motor having a casing, a piston slidably mounted in said casing and subjected to the pressure of fluid therein, means for connecting said piston and device, means for supplying desired equal increments of pressure to said casing and piston, and means for progressively increasing the movement of said piston in response to said equal pressure increments including a plurality of opposed springs interposed between the casing and connecting means, the springs acting in one direction being effective during the entire piston stroke and the springs acting in the opposite direction being effective during a portion of the stroke.

11. The combination with a source of fluid pressure and a device to be actuated, of a fluid motor having a casing, a piston slidably mounted in said casing and subjected to the pressure of fluid therein, anactuating member having a connection with said device, resilient means interposed between said casing and member for exerting a predetermined force thereon for maintaining the memberin retractedmosition and for opposing movement thereof throu h the entire stroke, resilient means interposed between the casing and member for exerting a lesser force on the member in the opposite direction during a portion of the stroke, and means for connecting said member and piston including a spring for opposing initial relative movement" therebetween with a force less than the difierence in the two first named forces.

casing for assisting said movement during said one portion of the travel.

13. A fluid actuator comprising a cylinder, a piston slidably mounted in said cylinder, a piston rod slidably mounted in the cylinder, a preloaded spring interposed between the cylinder and rod for normally maintaining the latter in retracted position in'the cylinder with a predetermined force greater than the normal friction force between the piston and cylinder, and means connecting said piston and rod for normally maintaining the piston in retracted position relative to the rod and for insuring initial movement of said piston prior to movement of said rod in response to the application of fluid pressure to the-cylinder including a, spring interposed between the piston and rod and a substantially frictionless lost motion connection between said rod and piston for preloading the second named spring to normally maintain the piston in said retracted'position with a force less than that exerted by the first named spring on the rod and greater than the normal friction force between v the cylinder and piston.

14. A fluid actuator comprising a cylinder, a piston slidably mounted therein, and means for opposing movement of said piston during one portion of the travel thereof with a force increasing at a predetermined rate and during an additional portion of the travel with a force increasing at a lesser rate including a spring interposed between said casing and piston for opposing movement thereof on application of fluid pressure to the cylinder, and a second spring interposed between the piston and casing for assisting said movement during said one portion of the travel.

15. A fluid actuator comprising a cylinder, a piston slidably mounted in the cylinder, a piston rod in the cylinder, resilient means interposed between the cylinder and rod for exerting a predeterminedv force thereon in one direction for normally maintaining the rod in retracted position and for opposing movement thereof during the entire stroke, resilient means interposed between the cylinder and rod for exerting a lesser force on the rod in the opposite direction during a portion of the stroke, and means for connecting said rod and piston including a spring for opposing initial relative movement therebetween with a force less than the difference in the two first named forces.

16. A fluid actuator-adapted to receive equal increments of fluid pressure comprising a casing, a piston slidably mounted in said casing, and means for progressively increasing the movement of said piston in response to said equal fluid pressure increments including a plurality of opposed springs interposed between said casing and piston, the springs acting in one direction being effective during the entire piston stroke and the springs acting in the other direction being efand casing for opposing movement thereof on application of fluid pressure to said casing, and a second spring interposed between said piston and fective during portions of the stroke,

ELLERY R. FITCH. 

